Shelf Sea Biogeochemistry blog

Friday, 28 August 2015

Worm holes and snail trails

My job on the RRS Discovery is to characterise the activity
of the species that live in the sediment.

I look at a process called bioturbation, which is when
species living in the sediment create burrows or move sediment particles up or
down.These activities stimulate
microbial growth and encourage the cycling and release of nutrients and are
important mediators of shelf sea processes.

To measure bioturbation we use coloured particle tracers we
call luminophores, which are placed on top of sediment cores we collect in a 2
– 3 mm thick layer.These are bright
coloured particles that can be easily seen when they are mixed into the
underlying sediment.

There are many small worms, shrimp and snails living in the
sediment that are constantly moving, grazing, hunting, burrowing, and
bioirrigating (moving water to keep burrows and the sediment oxygenated). They
can create vast networks of burrows such as those created by Nephrops norvegicus, the Norwegian
lobster. They can create mounds and pits on the sediment surface like the
Angular crab, Goneplax.

An Angular crab, which can create deep pits and large mounds
around a burrow network.

We photograph the sediment under ultra-violet light, making
the luminophore particles fluoresce so they can be easily identified compared
to the surrounding sediment by an automatic computer program and the number of
luminophore pixels per sediment depth calculated.

An example image of luminophore movement taken under
ultra-violet light.It is easy to see
where the luminophores have been moved by species activity. These trails have
probably been created by small worms creating burrows which the luminophores
have fallen down. This is an easy and effective way to measure species activity
in the sediment in the shelf seas and we can relate this activity to nutrient
fluxes measured over time.